Question I'm trying to recall presets via MIDI on the unit, but it does not seem to respond - what is going on

The M300 / M350 / G-Sharp does indeed receive program changes, but for them to be useful, some user presets have to be stored, as the unit otherwise does not contain any presets as such. The effect-selector knobs on the front are not presets per se, but you can control them sending MIDI CC 50 (for the multi effect) and 51 (for the reverb type) to the unit.